Methylenethioxophosphorane (thiophosphene) intermediates in the reactions of diphenylmethylphosphonamidothioic chlorides with amines. Differences between the elimination–addition mechanisms of nucleophilic substitution for P
S and P
O substrates
Abstract
In reactions with R2NH (R = Me or Et) in CHCl3 the PS substrate Ph2CHP(S)(NMe2)Cl differs markedly from its P
O counterpart: the rate of substitution is increased much more by a 4-nitro substituent but is also more sensitive to the bulk of the
S and P
O compounds both seem to react by elimination–addition mechanisms. It is suggested that whereas in the P
O case the conjugate base is formed rapidly and elimination of chloride to give the methyleneoxophosphorane (phosphene) intermediate is rate limiting, the conjugate base of the P
S substrate eliminates chloride rapidly giving a relatively stable